flashlight : Computer Hardware Buyers’ Glossary

A battery powered light. Usually the bulb is an LED (Light-Emitting Diode) or group of LEDs (Light-Emitting Diodes), but older
styles may use a small incandescent bulb. An LED is preferable since it will not burn
out and it generates more light for the same amount of power.

Small flashlights fit on a keychain to help you find the lock hole in the
dark.

Flashing lights you attach to pedestrians, bicycles and pets to make them more visible at night.

Medium size flashlights let you examine the inside of computers.

Full size flashlights let you find your way in the dark.

Supersize flashlights let you illuminate a campsite/tent for many hours. Often
gas-powered lanterns are used instead for this purpose.

Judging Quality

Look for the cells to be sealed in a screw-tight metal container, ideally
waterproof. Even atmospheric water can corrode the battery contacts.

The brightness should be specified in lumens. You
will find an order of magnitude difference in brightness with same battery voltage.
The advantage of low brightness is the battery will last longer.

Caveats

One problem with small flashlights is the tiny replacement batteries can often cost
more than a whole new flashlight. AA and AAA are relatively cheap. Lithium cells
are about $6 each. Others are $20 and up.

Sometimes flashlights are sold as suitable for keychain use that are either
ridiculously large or have no proper loop to attach the keychain. Read the size
specifications. Don’t just guess from the illustration.

Double check you are getting an LED not an ordinary incandescent bulb. It should be 80+ lumens.

Even on some high end lights, you can’t replace the bulb or batteries.

Lights that you turn by twisting the cap on tighter are easy to turn on by mistake, and drain the batteries.

Get a different model of flashlight for each set of keys. That ways the keys will be distictive.

Care

Before first use, treat the battery contacts with DeoxIT
to protect them from corroding.